This invention relates to a mobile radio system having a plurality of mobile terminals connected with a mobile switching center via an air interface for communication control and optionally for billing. In addition the invention relates to a method for operating mobile terminals of a mobile radio system.
In known mobile radio systems, for example the GSM network, the mobile terminals are usually connected with a mobile switching center via an air interface. The mobile terminals are controlled by a subscriber identity module. This subscriber identity module is usually designed in the form of a chip card in ID-1 or ID-000 format disposed removably in the mobile terminal. The subscriber identity module (SIM) is used inter alia for granting the authorized person access to the mobile radio network and permitting call accounting. For this purpose the SIM contains a subscriber identity (International Mobile Subscriber Identity IMSI) for identifying the subscriber world-wide in all GSM networks. The subscriber identity usually has the billing account assigned thereto through which call accounting is done.
In particular for double utilization of a mobile phone (e.g. for business and private purposes) it has proven advantageous to equip the subscriber identity module with at least one further identity. European patent specification EP 0 579 655 B1 discloses a method for mobile telephone systems controlled by subscriber identity modules each containing at least two alternatively usable identities. When beginning to operate the mobile unit the user can activate the desired identity through the insert direction of the subscriber identity module or by entering a personal identification number (PIN) via the keyboard.
The disadvantage of the known method is that the alternatively usable identities must already be stored in the card upon its issue. That means in practice that the number of alternatively usable identities must already be known when a mobile radio connection is applied for. In particular when a new identity is to be allotted later this can only be done by issuing a new card, i.e. a new subscriber identity module.
The problem of the invention is therefore to state a mobile radio system and a method for operating the mobile radio system and a subscriber identity module which avoid the abovementioned disadvantages.